Autism is a developmental disorder with impairments in language and communication as primary diagnostic criteria. Family studies of children with autism have noted similar features, or a "broader phenotype," in some first-degree relatives, including impairments in language functioning. Recent imaging studies in children with autism have found structural abnormalities in language association cortex, white matter overgrowth in areas underlying language regions, and evidence of underconnectivity between brain regions critical for complex language. We hypothesize that abnormalities in language-related cortex and decreased structural integrity of white matter connecting these regions are heritable neurobiological markers of language impairment in autism, and the heritable nature of autism suggests that siblings of children with autism may also exhibit these abnormalities. The proposed studies will provide insight into the etiology of language impairment in autism and will help to define genetic subgroups based on neurobiological markers that will complement existing behavioral phenotypes.